HDU 2962 Trucking

二分查找+最短路

二分限制高度，然后求最短路

#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;

const int INF=0x7FFFFFFF;
const int maxn=1000+10;
struct Edge
{
    int from,to,lim,len;
} e[maxn*maxn];
int N,M,tot;
int st,en,Lim;
vector<int>G[maxn];
int disLen[maxn];
int flag[maxn];
int Min,Max,Mid;

void init()
{
    for(int i=0; i<=N; i++) G[i].clear();
    tot=0;
}

void SPFA()
{
    queue<int>Q;
    for(int i=0; i<=N; i++) disLen[i]=INF;
    memset(flag,0,sizeof flag);
    disLen[st]=0;
    flag[st]=1;
    Q.push(st);

    while(!Q.empty())
    {
        int h=Q.front();
        Q.pop();
        flag[h]=0;
        for(int i=0; i<G[h].size(); i++)
        {
            int id=G[h][i];
            if(e[id].lim<Mid) continue;
            if(disLen[h]+e[id].len<disLen[e[id].to])
            {
                disLen[e[id].to]=disLen[h]+e[id].len;
                if(flag[e[id].to]==0)
                {
                    flag[e[id].to]=1;
                    Q.push(e[id].to);
                }
            }
        }
    }
}

int main()
{
    int T=1;
    while(~scanf("%d%d",&N,&M))
    {
        if(N==0&&M==0) break;
        init();
        for(int i=1; i<=M; i++)
        {
            int u,v,f,c;
            scanf("%d%d%d%d",&u,&v,&f,&c);
            if(f==-1) f=INF;

            e[tot].from=u;
            e[tot].to=v;
            e[tot].lim=f;
            e[tot].len=c;
            G[u].push_back(tot);
            tot++;

            e[tot].from=v;
            e[tot].to=u;
            e[tot].lim=f;
            e[tot].len=c;
            G[v].push_back(tot);
            tot++;
        }
        scanf("%d%d%d",&st,&en,&Lim);

        Min=0;Max=Lim;
        Mid=(Min+Max+1)/2;
        int ans1,ans2=INF;

        while (Min < Max)
        {
            Mid = (Min+Max+1) >> 1;
            SPFA();
            if (disLen[en] != INF)
                Min = Mid, ans2 = disLen[en];
            else Max = Mid - 1;
        }

        if(T!=1) printf("\n");
        printf("Case %d:\n",T++);
        if(ans2==INF)
            printf("cannot reach destination\n");
        else
            printf("maximum height = %d\nlength of shortest route = %d\n",Min,ans2);
    }
    return 0;
}